Multi-scale nature of composite materials: three case studies

Official URL: http://192.168.1.20/record=b1477537 (Table of Contents)

Science and engineering of fiber reinforced advanced composite materials (FRC) is an actively broadening research field with more and more emphasis on their multi-phase and multi-scale characteristics. While emerging manufacturing and characterization techniques provide ability to manipulate the materials at all scales from traditional macro to relatively recent emergence of nano-scale, computational tools provide better understanding of behavior of composite materials. Collective and coherent use of these abilities and tools can make composites better. This thesis is an effort to address how and why engineers can and should associate other characteristic scales with the traditional macro-scale engineering of composites. Three different studies on structural composites which exemplifies the need for multi-scale overlook are reported, each contained in individual chapters. Nano-Macro associated case study: In-house synthesized poly(styrene-co-glycidyl methacrylate) based nano-fibers manufactured by electro-spinning were implemented to carbon fiber reinforced epoxy composites as interlayers. As a result of several mechanical tests and fracture analysis a significant increase in resistance against mode II delamination (70%) and transverse matrix cracking (25%) with literally no weight penalty was observed. This increase was attributed to the chemistry tuned epoxy compatibility of nano-fibrous interlayers. Micro-Macro associated case study: A systematic statistical tool built upon an intensive amount of finite element analyses. Surrogate models on the micromechanics based stress amplification factors for CFRP reinforced epoxy composites are offered. Quadratic models are reported taking longitudinal fiber stiffness (Ef), fiber volume fraction (Vf) and matrix stiffness (Em) as input and calculates each term of the stress amplification matrix that can connect macro-level stresses to micro-level stresses. Meso-Macro associated case study: The fiber bundle width and inter-bundle distance of non-crimp fabric reinforcements (NCF) was considered. The effect of reinforcement architecture on the mechanical response was evaluated through the manufacturing and testing of vinyl ester based composite laminates containing glass fiber NCF of 300 TEX, 600 TEX, 1200 TEX and 2400 TEX yarn numbers with constant aerial weight. Overall results suggested that the inter-bundle distance was a tunable meso scale property that was effective especially under in-plane shear and longitudinal tensile loads.